[cfe-dev] Decls are not synonyms for the symbols they represent

[Ted Kremenek]

On Sep 17, 2008, at 9:50 AM, Argiris Kirtzidis wrote:

> This is what I think too, it's better if the AST is a simple as  
> possible, more higher level semantic information could be build on  
> top of the AST, instead of getting embedded in.

Agreed.  I was thinking of something more of the lines of what Steve  
mentioned in his last email.  Just a clean way to go from Decls ->  
unique identifier.

>
> For example, there could be a framework like the analysis framework,  
> that gets "fed" ASTs from multiple translation units and can reason  
> about declarations as a whole.

I've been thinking about doing this for a while, and it would be  
something needed for inter-procedural static analysis.  However, to  
me, this is a different concept that would be layered on top of  
whatever mechanism is in place to resolve identifiers/declarations  
*within* a translation unit.

The problem that I'm concerned with right now is that there are cases  
where two DeclRefExprs can refer to different VarDecls that correspond  
to the same variable, but a client of the AST has no way of knowing  
that that is the case.  Consider:

----

extern int x;

void foo() {
   x++;
}

extern int x;

void bar() {
   x++;
}

void baz() {
    extern int x;
    x++;
}

-----

If you do an AST dump of this, you will see that the DeclRefExprs for  
'x' in foo(), bar(), and baz() respectively refer to separate  
VarDecls.  Right now a client of the ASTs has no way of knowing that  
these VarDecls refer to the same variable.  Certainly a higher-level  
API that resolves identifiers across translation units could do this,  
but it might have to do a lot of work to resolve situations like the  
one above.  By having a mechanism to resolve identifiers within a  
translation unit, this higher-level API would much easier to implement.